1. Field of the Invention
The present invention relates to heart electrode leads of the kind having a proximal end to be connected to a heart-stimulating device and a distal end insertable via the vascular system into the human or animal heart. This kind of heart electrode lead is particularly suitable for intracardial stimulation of the heart with the help of an implantable pacemaker or defibrillator.
2. Description of the Prior Art
A large number of different heart electrode leads are known in the art. Such electrode leads have to fulfil many different requirements. One requirement is that the electrode lead is sufficiently flexible once it has been implanted in the human or animal body, such that it does not exert stress on or injure the body parts surrounding the implanted electrode lead. Another requirement is that the electrode lead is sufficiently rigid so that it may be inserted, for example via the vascular system, into a human or animal heart. Furthermore, it is sometimes required that the distal end of the electrode lead may be guided, during the insertion, to a specific position in the heart.
U.S. Pat. No. 5,487,757 describes a multicurve deflectable catheter. The catheter has an axial lumen in which a stiffener wire is slidably introduced. The stiffener wire, when advanced into a tip portion of the catheter, will give the tip portion and the stiffener wire a combined bending stiffness in order to give the tip portion a certain radius of curvature. The catheter may further include a core wire configured to rotate the deflectable tip about a longitudinal axis. The catheter further has a manipulator wire coupled to the distal end of the deflectable tip, whereby the deflectable tip may be deflected by axial force applied to the manipulator wire. The manipulator wire, the stiffener wire and the core wire are located in separate cavities arranged side by side at the tip portion. As a consequence of this arrangement, the flexibility of the catheter will depend on in which direction the catheter is bent.
U.S. Pat. No. 5,571,160 describes an electrode cable for use with a pacemaker. A tubular element can be slid on and off the electrode cable in order to impart a certain curvature onto the electrode cable. The electrode cable may be straightened by means of a stylet introduced into a channel of the electrode cable.
U.S. Pat. No. 5,170,787 describes a device for simplifying the positioning of electrodes inside living bodies. This device comprises a hollow lead in which a stylet wire combination is inserted. The stylet wire combination comprises an outer tubular member and an inner wire member. The inner wire member may have a preshaped curvature. By withdrawing the outer tubular member a certain distance, the inner wire member causes the distal end of the lead to take a curved shape caused by the curvature of the inner wire member.
Although it is possible to modify the stiffness of the above described electrode leads by withdrawing or inserting the different stiffening members, there is still a need to make it possible to further modify the stiffness of the electrode leads. In particular, it has been found that, when the electrode lead is being inserted into a human or animal body, it is sometimes desirable to withdraw the stiffening wire to a certain extent when the distal end of the electrode lead passes certain positions in the body. When the stiffening wire is withdrawn, it has been found that the portion of the electrode lead from which the stiffening wire has been withdrawn is sometimes too flexible. It should be noted that it is an advantage that the electrode lead is flexible once it has been inserted into its predetermined position in the body. Also during the insertion phase, it is sometimes an advantage that the electrode lead is very flexible in order to allow for a portion of the lead to be bent. One example when it is of interest to partly withdraw the stiffening wire is when the distal end of the electrode lead is introduced into the heart of a patient. However, when the stiffening wire is withdrawn, the distal end of the electrode lead may be too soft so that it is difficult to steer this end into position in, for example, the ventricle. Instead, the distal end of the electrode lead may have a tendency to follow the blood stream into the pulmonary artery.
It is an object of the present invention to provide a heart electrode lead in which the stiffness may be modified even when a guide wire is partly or totally withdrawn from the electrode lead.
This object of the invention is obtained by a member for modifying the stiffness of a heart electrode lead having a proximal end to be connected to a heart-stimulating device and a distal end insertable via the vascular system into a human or animal heart, the member being flexible, elongated and having a longitudinal cavity extending along said member, the member having an interior cross-sectional dimension defined by the cavity and an exterior cross-sectional dimension, the exterior cross-sectional dimension being such that the member is withdrawably positionable in a channel of the elongated heart electrode lead, and the interior cross-sectional dimension being dimensioned to allow a guide wire to be movably arranged therein.
When the member is positioned in the electrode lead, the electrode lead will be more stiff and thus less flexible. The member may thus be located in the electrode lead when the electrode lead is inserted via the vascular system into the heart. Even when no guide wire is positioned in the electrode lead, or when the guide wire is partly withdrawn, the distal end of the electrode lead will have a certain stiffness which makes it easier to position the distal end of the electrode lead at a certain position in the heart.
In a further embodiment of the invention, the outer boundary of the cross-section of the member is essentially circular. The member thereby fits into a corresponding circular channel in the electrode lead. Furthermore, since the cross-section is circular, the member and the electrode lead may be arranged concentrically such that the flexibility of the electrode lead will be independent of the direction into which the electrode lead is bent.
According to a further embodiment, the member is made of a non-metallic material. Such material will make it possible to make the member such that it is neither too stiff, nor too soft.
According to another embodiment of the invention, the material is a polymer. Such a material is particularly advantageous in order to give the member a suitable stiffness.
According to still another embodiment of the invention, an arrangement is provided at one end of said member for preventing the end of the guide wire from passing the end of the member. This embodiment has the advantage that the position of the member in the electrode lead may be modified by pushing said member with the help of a guide wire. Furthermore, according to this embodiment there is no risk that the guide wire extends beyond the end of the member.
According to still another embodiment of the invention, at least a portion of the member has a pre-set curvature. Since the member has a pre-set curvature, the electrode lead will tend to be bent according to this curvature. This makes it possible to position the distal end of the electrode lead at a certain position in the heart.
According to another preferred embodiment of the invention, the longitudinal cavity has an essentially circular cross-section and is adapted to allow a guide wire having a corresponding cross-section to be movably arranged therein. By this arrangement, the guide wire, the member and the electrode lead may be arranged concentrically such that the flexibility of the lead is the same in all bending directions.
According to still another embodiment of the invention, the longitudinal cavity has an elongated cross-section and is adapted to allow a guide wire having a corresponding cross-section to be movably arranged therein. Such an embodiment is advantageous if the flexibility is to be different in different bending directions of the electrode lead. This is, for example, the case when the distal end of the electrode lead is supposed to bend in a certain direction in order to make it easier to position the distal end of the electrode lead at a certain location in the heart.
The invention also provides an elongated heart electrode lead adapted for insertion via the vascular system into the human or animal heart, the heart electrode lead having a proximal end to be connected to a heart-stimulating device and a distal end having one or more electrode surfaces adapted to be inserted into the heart, the electrode lead having at least one electrical conductor adapted to electrically connect the heart-stimulating device to the electrode surfaces, a channel extending from the proximal end to a position at or close to said distal end, and a member according to any one of the above embodiments, positioned in the channel, the member being movably arranged in the longitudinal direction in the channel and the member being arranged such that it may be withdrawn from the channel via the proximal end.
According to the invention, there is also provided a guide wire arrangement adapted to be movably positioned in a channel in an elongated heart electrode lead having a proximal end to be connected to a heart-stimulating device and a distal end having one or more electrode surfaces to be inserted into a human or animal heart, the guide wire arrangement having a member according to any one of the above-mentioned embodiments, and an elongated guide wire movably arranged in the longitudinal cavity. According to this aspect of the invention, a guide wire arrangement suitable to be positioned in a channel in an elongated heart electrode lead is provided.
According to a preferred embodiment, the guide wire is a single elongated element. Such a guide wire is relatively easy to produce and, furthermore, can be made with a relatively small diameter such that it easily fits into the longitudinal cavity of the mentioned stiffness-modifying member.
According to a further embodiment, at least a portion of said guide wire has a pre-set curvature. By this measure, the electrode lead may take a corresponding pre-set curvature, whereby the distal end of the electrode end may be positioned at a predetermined location in the heart.
According to a further embodiment, the guide wire has an outer elongated tubular element movably arranged in the longitudinal cavity and an inner elongated element movably arranged in the tubular element. By such a double guide wire arrangement, the stiffness of the electrode lead may be modified further. Furthermore, the curvature of the electrode lead may be controlled more precisely by such a double guide wire arrangement. It should be pointed out that the tubular element does not, necessarily, have to have a circular cross-section. The cross-section may, for example, be elongated.
According to still another embodiment, the inner element has a preset curvature. The outer tubular element of the guide wire may be made to be stiffer than the inner element. Thereby the guide wire, and thereby the electrode lead, may be relatively straight when the inner element is positioned totally in the tubular element. However, when the distal end of the tubular element is withdrawn so that the distal end of the inner element protrudes from the distal end of the tubular element, the electrode lead may take a corresponding curvature. Thereby, the curvature of the distal end of the electrode lead can be precisely controlled.
According to still another embodiment, the tubular element has a pre-set curvature. This embodiment is an alternative to the previous embodiment. According to this embodiment, the inner element is preferably stiffer than the tubular element. Thus, when the inner element is withdrawn, the tubular element causes the electrode lead to bend according to the pre-set curvature of the tubular element.
According to still another embodiment, an arrangement is provided that one end of the member for preventing the end of the guide wire from passing said end of the member.